A technique for detecting the pupils of a subject can be used for line-of-sight detection in order for intension expression of a physically ahandicapped person or opinion communication in an environment where information communication by voice is difficult. The line-of-sight detection is generally performed by calculating a relative position between a center of a pupil taken by a camera and corneal reflection obtained by illumination light from a light source. Also, it has been studied that the pupil detection technique is applied to a pupil mouse that performs input to a computer or a game apparatus by movement of a pupil of a subject without using fingers, or the pupil detection technique is used for doze prevention technique or driving management technique in automotive technology.
As an example of such a pupil detection technique, the following Patent Literature 1 discloses a pupil detection device as follows. The pupil detection device includes a light source which irradiates with illumination light and a camera which picks up a light pupil image and a dark pupil image of a subject. The camera has a aperture disposed to face the subject to allow an image of the subject to be introduced to an imaging element, and the light source includes first light-emitting elements which are arranged along edges of the aperture on the outside of the aperture and emit illumination light having a first central wavelength and second light-emitting elements which are arranged adjacent to the outsides of the first light-emitting elements and has a second central wavelength longer than the first central wavelength. By using such a pupil detection device, the light pupil image is picked up while irradiating the subject with illumination light by the first light-emitting elements, the dark pupil image is picked up while irradiating the subject with illumination light by the second light-emitting elements, and a difference between the light pupil image and the dark pupil image is calculated. Since pixel values at a position of the pupil of the subject in the light pupil image and the dark pupil image are significantly different from each other and differences in pixel values at positions other than the pupil of the subject are small, it is possible to detect the position of the pupil of the subject by calculating a difference in pixel values between the light pupil image and the dark pupil image.
There has been known various arrangements of light sources in the pupil detection technique using the light pupil image and the dark pupil image. For example, in a pupil detection device described in the following Patent Literature 2, a light source capable of irradiating with light from the inside of an aperture of a camera is provided, the light source includes a first illumination light source, having a first wavelength component that makes a bright pupil by reflection in a subject's pupil, and a second illumination light source having a second wavelength component that makes a dark pupil by reflection in the subject's pupil, and change of optical paths are made such that independent optical axes of the first illumination light source and the second illumination light source both coincide with an optical axis of camera means.
In a pupil detection device described in the following Patent Literature 3, light from a first illumination light source, having a first wavelength component that makes a bright pupil by reflection in a subject's pupil is emitted from the inside of an aperture when seen from a face side of the subject, and light from a second illumination light source, having a second wavelength component that makes a dark pupil by reflection in the subject's pupil is emitted from a plurality of positions which are adjacent to the outer periphery of the aperture and are rotationally symmetric to each other.
In a pupil detection device described in the following Patent Literature 4, a plurality of light-emitting elements are arranged along edges of an aperture of a camera, and the light-emitting elements include a first light emission source which emits illumination light having a first central wavelength and a second light emission source which emits illumination light having a second central wavelength longer than the first central wavelength.